A Study on the Diffuse Mechanism and the Barrier Property of Copper Manganese Alloy on Tantalum

In this paper, the electrical and material properties of CuMn/silicon oxide (SiO₂) and CuMn/tantalum (Ta)/SiO₂ were investigated, and an optimized concentration of Mn in the CuMn alloy as barrier layers in these two structures was also determined. CuMn alloy (0~10 atomic % Mn) deposited on SiO₂ and Ta were used in this paper. A diffusion barrier layer self-formed at the interface during annealing, and the growth behavior was found to follow a logarithmic rate law. The microstructures of the CuMn films were analyzed by transmission electron microscopy and could be correlated with the electrical properties of the CuMn films. After thermal treatment, only Cu-5 at.% Mn/ SiO₂ successfully avoided the diffusion of Cu atoms. Thermal stability of the films grown on Ta/SiO₂ was found to be better than that on SiO₂. When a Ta layer was added, the Mn atoms diffused not only to the interface, but also to the grain boundaries in the Ta layer and the interface between Ta and SiO₂. This phenomenon could be explained by the surface energy. As the thickness of CuMn shrunk from 150 to 50 nm and the sample was covered with a 100-nm-thick Cu layer, the amount of Mn atoms increased at the interface of CuMn/Ta. This is because the Cu layer had higher chemical potential which induced the Mn atoms to move toward the Ta layer and reduced the amount of Mn atoms in Cu after heat treatment.